Cathode ray scanning apparatus



Jan. 25, 1944. w. A. KNooP 2,339,853

" CATHODE RAY SCANNING APPARATUS Fild July so, 1942 s sheets-sheet 1 llll lllll lwga/ron WA. k/voo/ Jan. 25, 1944. w. A. KNOOP CATHODE RAY SCANNING APPARATUS K s Sheets-Shet 2 Filed July 30, 1942'" l lA/VA/TOR WA. K/VOOP AT TORNEV 5 Sheets-She at 3 %asEc FIG-4.

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w. A. KNOOP CATHODE RAY SCANNING APPARATUS Filed July 30', 1942 Jan. 25,1944.

V, P E R m m 0 M .1 WW 6 WA W w Patented Jan. 25, 1944 cA'rnonn RAY some srrm rus William A. Knoop, Plainfield, N. 1., asslgnor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application July 30, 1942, Serial No. 452,94!

(Cl. 1'l8'l.2)

3 Claims.

This invention relates to cathode ray scanning apparatus and particularly to a circuit for supplying deflecting current to deflecting coils of a cathode ray scanning devic from a push-pull amplifier. I

For the purpose of supplying an amplified electric wave to a pair of deflecting coils of a cathode ray tube, it has been found advantageous to employ push-pull amplification in the amplifier stage which supplies energy to the coils in order to balance out second harmonic distortion. When, for example, th vertical deflecting coils on opposite sides of a cathode ray tube of the image dissector type are connected in the anode circuits of the two amplifier tubes, respectively, of the push-pull amplifier in a manner to cause the vertical deflection of the cathode ray beam in response to a deflecting electromotive-force applied to the amplifier input circuit, it has been discovered that the dissector tube produced a dis,- torted image current. This distortion was found to be due to the distortion of the electron image produced in the dissector tube as a result of the opposing electromagnetic fields, set up by the vertical deflecting coils on opposite sides of the cathode ray tube, respectively, when energized 3y theanode currents from the push-pull ampli- For the purpose of avoiding distortion of the electron image in accordance with the present invention, the deflecting coils are caused to 'pro- 1 duce aiding magnetomotive forces when energized. The coils are included in a current path connecting the anodes of the 'push-pull'amplifier I tubes and there is provided a second current path connecting the anodes. through diilerent portions of which anode currents are supplied to different tubes, respectively of the push-pull amplifier. The resistance of the two portions of the second current path is such-that the current flowing through said deflecting coils is reduced to zero or a low amplitude when the control grids of the push-pull amplifier tubes are at the same potential.

In accordance with the invention means are provided for scanning alternatively still pictures or continuously moving motion picture film. In order to avoid the scanning of any part of the frame lines which separate successive picture portions of the motion picture film during the pic-.

ture scanning periods, that is, during the periods between successive vertical synchronizin intervals, the electron beamis deflected to cause the electron image in the dissector tube to move vertically through a short distance in the reverse direction with respect to the direction of mo-- a still picture which may be a single frame of a stationary motion picture film, the amplitude of the vertical sweep current is increased by reducing the capacity in the circuit of the vertical sweep generator and ,the direction of the defiecting current in the vertical sweep coils is si multaneously reversed.

Figs. 1 and 2 of. the drawings, when Fig. 1 is placed above Fig. 2, constitute a diagrammatic view of a cathode ray scanning apparatus in accordance with the present invention; and

Figs. 3 to 6 are diagrams to which reference will be made in describing the invention.

Referring to Figs. 1 and 2 of the drawings, there is disclosed a scanning apparatus comprising'a cathode ray tube l of'the image dissector type. A motion picture projector and a still pictur projector are mounted upon a carriage H which is slidable along the rods I2 and I3 passing through-lugs ,IQ and I of the carriage so that images may be projected from the motion picture film it or from a still picture I1, alternatively. to the cathode l8 of the dissector tube It. The motion picture projecting apparatus comprises a synchronous motor l9 energized from the 60-cycle source for driving the film sprocket 2| through the gears in gear box 22. Light from source 23 i directed upon the portion of the picture film within the film gate '24 by condenser lens 25"and a projector lens 26' projects an image of the portion of the fllm'within the film gate' upon the cathode i8. Similarly, when the carriage is moved to bring the still picture into alignment with the image dissector tube,

light from source 21 passing through condenser lens 28 illuminates the picture l1 and an image thereof is projected upon the cathode l8. Electrons emitted from the elemental areas of the cathode ill in accordance with the illumination thereof are focussed, dueto the electromagnetic field set up by current from source 29 flowin through coil 30, to form an electron image corresponding to the optical image on the cathode at the plane of a scanning aperture 3|. When a motion picture film is scanned the movement of the optical image on cathode l8 due to the movement of the film causes the electron image to move vertically'with respect to the scanning aperture 3|. The cathode ray beam from the cathode I8 is also deflected both horizontally and vertically to cause the movement of the electron image with respect to the scanning aperture 3|.

, To produce the horizontal deflection of thecathtion due to the movement of the film while the picture area is being scanned and rapidly in the same direction during. thevertical synchronizing period. To condition the apparatus for-"scanning ode ray beam, a saw-toothed wav current of line scanning frequency issupplied to the horizontal deflecting coils 32, 33 from a horizontal sweep circuit 34. To produce the vertical deflection of the cathode ray beam, a saw-toothed wave of field scanning frequency is supplied to the vertical deflecting. coils 8!, 3621mm therpushcroplirler 31, 88 or the vertical sweep circuit ,The electrons tromthe elemental areas in sucf cesslon oi the electron image which pom through LfliT'iZ aperture .8! due to the-horinmt l and vertical motion or the electron image born herd the first multiplier electrode of the electron multiplier 81. he s result, an image currentis set up in the terminating impedance-88 connected to the output of the electronmultiplier and this image ct may be liiled prior to its tranc to en im ge producing apparatus bythe amplifier 38., Suitable tials are applied to the electrodes of the image disaector time and its essocieted electron multiplier from the cimllit comprising batten? 39, condensers 8i and resistorsiid he is shown and described in. en application oi A. G. vlemen, Qerlsl No. 821,390, filed February 29, lulu (Patent No. 2291323, granted Aug. e, leer.

The motion picture film id me be advanced st the retc of sixty picture fr s per second,

for example, end theelectronimegemey be moved horizontally under control of the sew toothed were from sweep circuit 8 3 to ceuse successive linesv of the image to be s-cd at the,

rate of were lines per second or 220 lines per film frame, the ofelternute iremes being interlaced. 'ilny, suitable means may be employecl for supplying deflecting currents of saw-- toothed wave form to the horizontal deflecting coils s2, 83 and, if desired, these soils may be energized from spush-pull amplifier in the same manner that the vertical deflecting coils 3.8, 36 are energized, as be describedhereinsiter.

The means vfor energizing the horizontal defleeting coils 32, 88 shown diagrammatically-in Fig. 3 comprises a 26,460-cycle controlled oscil later 40 from which is derived by successive steps the submultiple frequency sources 4| and 82 or 13,230- cycle and 60-cycle waves, respectively, oi rectangular wave form. The BO-cyclewaye from the power source in and the Gil-cycle we've from the submultlple frequency generator are impressed upon the frequency regulating circuit 43. There is produced by the circuit 43 as the result oi beating together the waves from sources and 42 a control current which isv impressed upon the oscillator 40ior maintaining the frequency of the wave produced by the oscillator 40 in step with the frequency or the oil-cycle power source loythat is, for maintaining the frequency of source 40 at the 441st multiple or the frequency of power-source Ill. "Of course, a

line scanning frequencyrate other than 441 lines tor two picture frames of the film I. or

tor two field: scannin'gs-fotlthe 'etill picture l1 may be used in which case the frequency or under control or the subhermonic generator 42 are impressed by way of the 72-ohm coaxial line 4Q upon a. circuit for controlling the eneror the vertlcal sweep coils 35", 36. The

coaxiul line is terminated in a 72-ohm resistor 4? across which is connected a. 2,000-ohm potentiometer 48.. The 60-cyc1e impulses from the potentiometer. are impressed upon the control.

grid-cathode circuit oi the pentode having a cathode 6|, control current path for the pentode may be traced from the positive terminal or battery it through transformer winding W to model and horn cathode 5! through LOOO-ohmbiasing resistor Bl ,shunted by'l microlarad condenser 59 to the" grounded negative terminal of battery Eli Poeitire battery from source 56 is also supplied to screen grid 53 through 2,000-ohm resistor 68,. A icy-mess condenser d! or 1 microfsred is connected between the screen grid and ground.

' The suppressor grid '54 is connected to the cathode.

Trimmer windings 632 ,and G3 are electromagnetically coupled to the winding 51." The winding 62 is connected between the positive terminal of battery 58 and the anode 64 of s three=electrode vacuum tube .65. The winding 53 is in a, circuit connecting the grounded cathode 66 with the grid 61' of tube 66, the 0.1 microfarad condenser 88 shunted by LOW-ohm variable resistor as being connected in this circuit between the grid 87 and the winding GI.

Theimpulses impressed upon the control'grid c2 of the pentode in are of such polarity as to decrease the anode current or the tube flowing through transformer winding I! and the winding 63 is so wound with respect to winding I! that there are induced in winding 63, due to the impulses'in winding 61, impulses of electromotive force which make the grid 81 positive with respect to the cathode 60. As a result, electrons from cathode l8 accumulate on grid 6'1 and the condenser 63 becomes charged, the plate connected to the grid 61" being negative; The positive impulse impressed upon the grid 61 priorto the charging of condenser 8| causes a. sudden source 40' would be maintained at some har- I RCA Institute TechnicalPr-ess, Varick Street,

- New York, New. York. The HMO-cycle source 4| controls a lam-cycle impulse generating circuit 44 which, in turn,, controls the-horizontal sweep circuit u for c.13380-ey'cle saw-toothed current were to the horilontal de- ,flecting' coil: as,

- eixtr mm ore. member the "ne rush of abode current through transformer winding 82 totake place and, as a result, the voltage induced in winding 83 is increased to increase the positive potential on the grid '1.

At the'end of the-impulse from-the pentode 84,."

the grid 61 has a negative potential with respect to cathode 60 due to thecharg'e stored in condenser 48 end, a. result, no current flows through the anode circuit or tube 6|. Prior-to thetime theta succeeding impulsererrives from the pentode II, the condenser 00 has'pgrtlydlscharged through resistor and, when the'uxcceeding impulse arrives, action above. de-

scribed is repeated.

, The positive impulres'produeedat the termini of winding 43- which 'ls connected tocondenee'r 04 are also impressed througn condenser 14 upon the grid II or three-electrode vacuumitube'll. The node I! of tube 12 is connected to the positivetermiml of battery It while the cathode 14' is connected through condenser ll 010.25 microd ll-comes -lsrldtogroundr Eachimpulseon -modecurrenttoflowthroughacircuitincluding themeepoondeneer II to cause e charged. The m ll is connected throughegridleak'resiatorlltoground.-p

'" name-=10 .ir a constant" current tube v (152, screen grid", suppressor grid 54 and. node 55. The anode" node, 8|.

' sistor I08 to ground.

. assaecs 18. screen grid 19, suppressor grid 80 and an anterminal of condenser while the cathode 11 is connected to ground through a variable resistor 83 which may be adjusted to control the rate of discharge of condenser 15. The grid 18 is directly connected to ground. The screen grid 19 isconnected through 1 microfarad condenser 89' to ground, this condenser being shunted by a 50,000-ohm resistor 95. The positive terminal of battery 55 is connected to the screen grid 19 through 200,000-ohm resistor 89. The sup pressor grid 80 is connected to the cathode 11. Due to the charging of condenser 15 at a rapid rate and its slower discharging at a constant Anode current is supplied to tube 81 through 'a With the switch m m the position shown a saw- The anode is connected to the positive circuit from positive terminal of battery 59,

50,000-ohm resistor 92 to anode 90 and from cathode 88 through bias resistor 93 of 3,000-ohm and 50,000-ohm resistor 94 to ground. A grid tetrodes 31. and 38. The tube 31 has a cathode 99, a grid 91. screen grid 98 and an anode 99 and tube 38 has a cathode I00, grid IOI,' screen grid I02 and 'an anode I03. Anode 90 of tube 91 is connected to grid 91 through condenser I00 of 1 microfarad, and the lead connecting resistors 93 and 94 is connected through condenser i 05 of 1 microfarad to the grid IOI. Screen grids 98 and I02 are connected to the positive terminal of battery 59. A grid leak resistor I 09 of 0.5 megohm is connected between grid 91 and ground and grid leak resistor I01 of 0.5 megohm is connected between grid IN and ground. cathodes 99 and I00 are each connected to a terminal of 200-ohm resistor I00, the other terminal of which is connected to'ground. With the switch I I5 in themsition shown in the drawings. there is connected thus supplied to tube 31 through a circuit which may be traced from positive terminal of battery 59 through. a portion N1 of resistor IIO, winding I09 through switch I I5 to anode 99 and from cathode 95 through resistor I08 to ground. The anode circuit for tube 38 may be traced from positive terminal of battery 59 throughportion II8 of resistor IIO, winding III through switch II5 to anode I03 and from cathode I00 through re- With the switch I I5 in the position shown, the vertical deflecting coils 35 and 39 in series are in, a second current path connecting the anodes 99 and I03, a terminal of coil "being connected to'anode 99 and a terminal of coil"'39 being connected to anode I03.

toothed wave current of large amplitude as shown in the lower portion of Fig. 4 is caused to. flow through the vertical sweep coils and 39 and the apparatusis in condition for scanning the steady picture I1. When switch H5 is operated to close the contacts which are shown open in the drawings, the phase of the deflecting current through the vertical sweep coils is reversed because a terminal of coil 35 is then connected to anode I03 and a terminal of coil 38 is connected to anode 99. Moreover, 1 microfarad condenser I20 is connected in parallel with sweep condenser 15 so that a deflecting voltage of relatively small- -er amplitude will be produced due to the charging and discharging of condensers 15 and I20 in parallel. As a result. a deflecting current, as shown at the lower portion of Fig. 3, is produced in the sweep coils 35 and 39.

As shown in Fig. 3, the picture portion of a motion picture frame occupies about 85 per cent of the frame height and a black bar which "separates successive picture portions occupies about 15 per cent of the frame height. If the vertical scanning motion of the optical image on cathode l8 and the corresponding motion of the electron image were due entirely to the movement of the motion picture film, only 85 per cent of the total time would be spent in scanning the electron images corresponding to picture portions of-the film. The interval allotted for transmitting vertical synchronizing signals is usually less than 15 per cent of the total time, say 10 per cent. In

order to avoid lossof 5 per cent of the scanning d flected vertically in a manner to reduce the rate of movement of the electron image while a between anode 99. of tube 31 and anode I03. of

picture portion of the film is scanned by such an amount that the picture portion is scanned during 90 per cent of the time, leaving 10 per cent of the time for sending vertical synchronizing signals during which interval the electron beam vertical deflecting wave has a portion I2I of negative slope during 90 per cent of the film frame scanning period of let second and'a portion I22 of positive slope during 10 per cent of the period of /a0 second.

When scanning the still picture I1, the sawtoothed current applied to the vertical deflecting coils is increased in amplitude and reversed'in phase with respect to the current wave shown in Fig. 3. This wave is shown in Fig. 4 and comprises a portion I23 of positive slope having a duration of 90 per cent of second and a portion I24 of negative slope having a duration of 10 per cent of let second.

' The advantage or the arrangement shownin Fig. 2 for supplying energy-from the push-pull amplifier 31, 39 to the deflecting coils 35 and 35 which are on opposite sides of the image dissector tube may be understood from a consideration of Figs. 5 and 6. In Fig. 5, anode current is supplied to the tube 31 of the push-pull amplifier may be set up due to the currents flowing through coils 35 and 39 when a deflecting wave is applied to the input of the push-pull amplifier, as in Fig.

2, the coils 39 and 39, when connected as shown in must bewound so as to set Ina-opposing magnetomotive iorces when ene by current irom battery Ii. I Due to'the steady direct currentcomponent whiclrflows through coils II and 38 independently or any saw-toothed deflecting wave applied to theinput circuit push-pull amplifier '31, 38, there are set up by coils 35 and lliandtiinseriessothatthelargerporticnoi compared with the of detectingcoils .the alternating component 01' the sweep current irom amplifier 31, "will flow through the deflecting coils. current wave through coils 36 and II, theratio or inductive reactance to resistance of the im- 38 fields which deflect portions 0! the cathode ray v to cause thc'clectron image produced by the cathode ray beam to be distorted in the manner shown in Fig. 8.

Consider that only steady direct current mins-through the coils-3| and It to produce fields as indicated by the lines 1 5,135, F: and F4 oi Fig. 6.

Consider-also that the positive direction 01 the 1.

cathode ray beamcurrent C. R. is toward the observer viewing Fig. 6, then the forces acting upon the edge portions of the cathode my C, R.

i will be as shown by the solid arrows and the'beam will be d into the shape To avoid thi distortion oithe electron image the vertical sweep coils l8 and it are (energisedv iromithe push-pull ampliflercircuit in a manner to produce aiding magnetomotive forces. s'lherelfore steady direct 'current-doesnot flow through the cells 85 and 38 except for a small amount which may be used for centering the cathode ray beam, amount being adjustable by means oi the movable contact Ill, tor example. When shown by the dotpedance oi the current path-consistingot wind: kids it! and lliand resistor I1. is made equal to the ratio oi-inductlve reactance to resistance of cells 85 and; II so thatthe impedance ratio of the two current paths which are in shunt with respect to each other may quencies. A

What is claimed is: '1. Means for energizing the sweep coil of a cathode ray tube for producing an electromagnetlcfield for deflecting the cathode ray beam generated in the tube comprising a first con denser, means for alternately charging and discharging said condenser to generate an electromotive force across said condenser tor controlling the deflection oi said cathoderay beam, a pushp ll amplifier under control or said electromotive force, means for connecting the, output or said amplifier to said. sweep coil to cause an energising current to flow therethroush. a second conno deflecting wave is to the input or the push-pull amplifier 81, 88 of Fig. 2 and the control grids I! and III are, therefore, at substantially the same potential, the voltage measured between contact H6 and anode I! is substantially equal to and opposite to the voltage measured be- 7 age measured between anode 98 and anode in, that is, the voltage across coils and 38. is substantially hero. When a deflecting wave is applied to the input of the push-pull amplifier, current will new in opposite directions alternately through coils l5 and It, the current fiowat any instant being in such direction that aiding magnetomotive forces are set up by the coils and It. thus avoiding distortion of the electron image. With switch vl II in the position shown, at an in stant when the grid .7 is positive with respect to ground and grid Ill negative with respect to ground, the amplitude of the anode current for tube II will be greater the anode current Jot-tube 38 with the result that the voltace measure d between contact Ill and anode la is greater. than the voltage measured between contact HI and anode ill. Therefore, current will fiow from the positiveterminal or battery it through portion ill or resistor Ill, winding Ill, coil 3!, coil SI, to anode l9 and from. cathode I through re.

sister I 'toiground. At another instant when 1 grid III is positive and grid .1 negative with spect to ground, current from source II will fiow through'portion 1 0t resistor llli, l ll, coil 'il, coil 3! to anode II! and from-cathode amplifier is" caused to flow through coils II and It for producing an electromagnetic field for vex-- ticslly. deflecting the cathode ray beam while avoiding distortion oi the electron image.

The impedance of the current path consisting of windings I and Ill and resistor H0 is high tween contactv H8 and anode its so th'atthe'volt- Ill through resistor I" to ground. Thusfa sa'wtoothed current wave supplied by the push-pull first current path being large with respect to the denser, and switching means which may be operated to reverse the phase of said m: current and to simultaneously connect said second condenser in parallel to said first condenser to decrease the ampltiude of said energizing urrent.

2. Means for scanning alternatively a continuously moving motion picture film or a still pic-.

ture, comprising a cathode ray scanning device having means for generating a cathode ray beam, means for repeatedly deflecting said beam horizontally at the line scanning rate, means 101' gen crating an electromagnetic field i'or repeatedly vertically deflecting said cathode ray beam at the field scanning rate when suitably energized, means for supplying to said vertical deflecting means for energizing it asaw-toothed current wave 01 such slope and amplitude-that the period 0! scanning the picture portions of the continu 'ously moving film is increased, and means for increasing the amplitude and simultaneously revhaving inductance and resistance, a'contact to said current path the position of which maybe varied, a source of direct current in a current path connecting said movable contact and said cathode, means-tor producing an electromagnetic field for deflecting said cathode ray beam when suitably energized, and means ror connecting said last-mentioned means in a second current path connecting said anodes, the impedance or said impedance 01' said second current path and the ratio of said impedances being substantially constant over a wide range of frequencies.

In order to avoid distortion of the a be the same at-all ire- 

